The story of Death by Lightning commences in 1969, as workers at the Army Medical Museum uncover the preserved brain of Charles Guiteau, wonderment etched on their faces as they ponder his identity. The narrative shifts to 1880, in the bustling heart of New York City, where Charles sits before a jury, assessed for his transgressions after a spell in confinement. The judge reads aloud a letter from Charles' estranged father, declaring him guilty of theft, deceit, and fraud. Charles vehemently denies each charge and is released. As he exits, he boldly declares his capacity for greatness, including the presidency of the nation.
Simultaneously, James Garfield, a congressman hailing from Ohio, is summoned to Chicago to speak on behalf of the presidential candidate, John Sherman. James embarks on his journey, where he crosses paths with Sherman at a restaurant. Sherman commends James for his bravery and perseverance during the war in Tennessee, and in turn, shares tales of President Grant and his senator, Roscoe Conkling, who are also present at the dining establishment.
Meanwhile, Charles' sister, Frances (Franny), fetches him from prison and brings him home. Charles harbors aspirations of revitalizing his life by starting a newspaper venture and implores Franny to helm the arts section of The Daily Theocrat. However, Franny's husband, George, is displeased with Charles' return and engages in an argument with his wife over harboring her criminal sibling.
Charles ventures to a bank in Chicago to apply for a loan for his newspaper endeavor but is summarily dismissed after previously striking the bank manager with a paperweight. Upon leaving the bank, he encounters President Grant, Roscoe, and their acquaintance, Chester. Roscoe and Chester treat Charles with disdain and disrespect. Back at Franny's abode, Charles fabricates a lie to his sister and brother-in-law about securing his loan sanction. While they congratulate him in public, George whispers to Charles that Franny would be better off if he maintained a distance.
Concurrently, James encounters Mr. Stockton, a war veteran who resides on the streets. Mr. Stockton recounts how he lost his leg and both sons in the war's frontline. Despite having nothing left for himself, he vows to continue fighting for his country.
James extends his hospitality, offering his bed to Mr. Stockton while he sits down to pen the speech for Sherman. The following day, James embarks on his journey to the convention center, where Roscoe speaks on behalf of President Grant, igniting a frenzied cheer from the crowd that shakes the very foundations of the competition. The other candidates, feeling the weight of this overwhelming support, can only fidget in their seats.
James's mind drifts back to his earlier conversation with Roscoe, where the senator had derisively dismissed James's decision to come to Chicago instead of maintaining a low-profile life in Ohio. In his speech, James speaks passionately about the struggles of the common folk in America and how he empathizes with their plight. The crowd is moved to tears, some even suggesting that he run for office himself.
Meanwhile, Charles is consumed by his own demons, chopping wood to drown out the noise in his head. Franny watches him with concern, worried for her brother's well-being. In Chicago, the voters cast their votes, but even after thirty-six attempts, there is still no clear majority. Some voters begin to shift their allegiance to James, causing Sherman to fret.
The next morning, Charles apologizes to Franny for his outburst and they engage in a heartfelt conversation about their childhood. Franny's revelation that George plans to send him to a mental health facility shocks Charles, and he leaves her house, ending up outside the convention center amidst the chaos of a still undecided majority.
Inside, the tension builds as one by one, the other candidates relinquish their seats to James. Eventually, James gains a majority and defeats President Grant. Roscoe accepts the decision publicly but in private whispers to Chester to have James eliminated.
Unhappy with the outcome of the election but nonetheless forcefully elected as the new Presidential candidate, James makes his way to his hotel when he runs into Charles. The two men shake hands, and Charles, along with the other people in the crowd, cheers James on.
The episode concludes with George and Franny learning the devastating truth that Charles had stolen all their money before fleeing to Chicago.
